It is a relatively recent discovery that a colony of Campylobacter pylori bacteria is usually found associated with gastritis and duodenitis, and is frequently found at the sites of peptic and duodenal ulcers. (Coelho et al: "Campylobacter pylori in Esophagus, Antrum, and Duodenum", Digestive Diseases and Sciences, Vol. 34, No. 3 (Mar. '89), p. 445; Bartlett: "Campylobacter pylori, Fact or Fancy", Gastroenterology, Vol. 94, No. 1 (Jan., '88), p. 229). Suitable medication for combating the bacteria is known, but it is important that there be a reliable test for its presence so that proper treatment is assured, progress of the treatment can be monitored, and methods of eradication can be assessed.
Heretofore the most frequently employed technique for determining the presence of C. pylori and disease conditions associated with it has involved the insertion of an endoscope into the stomach, after administration of a suitable sedative to the patient, for direct visual examination of the gastric mucosa tract and/or withdrawal of a biopsy specimen. This procedure required a high degree of skill on the part of the person performing it, subjected the patient to some risk of injury, and was in any case uncomfortable for the patient. Thus a noninvasive technique for diagnosing ulcer or determining the presence of C. pylori is very much desired, as pointed out by Bartlett, supra, and by Evans et al: "A Sensitive and Specific Serologic Test for Detection of Campylobacter pylori Infection", Gastroenterology, Apr., 1989, p. 1004.
Graham et al reported successful results with a breath test wherein patients first ingested urea labelled with carbon-13, a stable, naturally occurring non-radioactive isotope. In the presence of urea, C. pylori produces urease, an enzyme that breaks down urea into ammonia, carbon dioxide and other products. Graham et al found that for persons confirmed by other tests to have C. pylori infections, .sup.13 CO.sub.2, derived from the labelled urea, was present in the breath in readily detectable and substantially constant quantities during the period from about 20 minutes to about 100 minutes after the ingestion of the urea; whereas little or none of the labelled CO.sub.2 was found in the breaths of persons confirmed as free of C. pylori. ("Campylobacter Pylori Detected Noninvasively by the .sup.13 C-Urea Breath Test," The Lancet, May 23, 1987, p. 1174).
A major disadvantage of the technique employed by Graham et al is that detecting the presence of the isotopic CO.sub.2 requires the use of a complicated and expensive mass spectrometer, which is not available to many hospitals and is unlikely to be found in a clinic, much less in an individual physician's office.
Bell et al reported successful use of a generally similar technique wherein the ingested urea was labelled with carbon-14, which is radioactive. The labelled .sup.14 CO.sub.2 appearing in the patient's breath was detected with a scintillation counter. (".sup.14 C-Urea Breath Analysis, a Non-Invasive Test for Campylobacter Pylori in the Stomach", The Lancet, June 13, 1987, p. 1367). Bell et al pointed out that the scintillation counter required for their .sup.14 C breath test is inexpensive and readily available, but it is by no means cheap. More important, both diagnostician and patient will obviously be uncomfortable with the thought of ingesting radioactive material, even in low radioactivity doses; and, indeed, Evans et al, supra, while pointing out the need for a simple and reliable noninvasive test, expressly mention "the undesirable radiation exposure associated with the use of .sup.14 C-urea". A breath test certainly offers the possibility of a comfortable noninvasive diagnosis, but heretofore it has clearly not been obvious to those skilled in the art how a reliable breath test can be made without requiring the ingestion of urea containing a labelled element-- which is therefore relatively expensive in itself--and without the need for expensive apparatus for detecting the labelled element.
Underlying the present invention is the known fact that the local production of ammonia after ingestion of urea is a reliable indication of the presence of C. pylori. The invention proceeds from the theory that at least some portion of the generated ammonia is absorbed into the blood stream, passes through the liver without being broken down there, and is delivered to expired air at the alveoli of the lungs. On this basis, detection of trace amounts of ammonia in expired alveolar air would afford the possibility of a simple and inexpensive noninvasive test for C. pylori.
However, ammonia cannot be detected in expired alveolar air with the conventional apparatus that it is obvious to employ for the purpose. This fact has heretofore tended to cast doubt upon the underlying theory of this invention, especially when taken with the fact that the liver effects a substantial detoxification of blood passing through it and might therefore be assumed to remove ammonia from the bloodstream.
However, the applicant has discovered that it is not because of the absence of ammonia that no ammonia has heretofore been detected in the breath samples of confirmed gastritis and duodenitis patients challenged with urea, but because of the instability of ammonia in expired alveolar air. This instability is due to the relatively large quantities of water vapor and carbon dioxide in that air.
Immediately upon being expired, the breath is a mixture of gases that is at or near body temperature, having a water vapor content that is at the saturation value for that temperature. Any surface that is to be contacted by those breath gases for the purposes of ammonia detection is almost necessarily at a lower temperature. On any such surface, therefore, some condensation of the H.sub.2 O content takes place. Because ammonia is readily soluble in water, the condensate water droplets tend to absorb the ammonia, and the CO.sub.2 reacts with the ammonia solution to form ammonium bicarbonate, which is for practical purposes removed from the air. Owing to inevitable delay between the time of exhalation and the instant when the breath sample is presented to the ammonia detection means, the amount of gaseous ammonia in the breath sample, which was only a trace quantity in the first place, is reduced to a virtually undetectable level.